1. Field of the Invention
The present invention relates to a resolver/digital converter, and more particularly to a small-sized and low-cost resolver/digital converter having noise immunity.
2. Description of the Related Art
In a servo control system, a rotational angle sensor is required to detect a rotational angle and to perform feedback control. In control of a brushless motor, a rotational angle sensor is also required because of the necessity of supplying a current to a motor coil depending on a motor rotational angle. Thus, the rotational angle sensor is required in not only the servo control system, but also in other systems. As the rotational angle sensor, a resolver has hitherto been widely used from the advantageous features of robustness and environment resistance which are attributable to its simple construction.
Further, a resolver/digital converter has been developed which is used to convert a signal from the resolver to a rotational angle and to input the rotational angle, as digital data, to a microcomputer, etc. (see Patent Document 1; JP-A-2000-353957, Patent Document 2; JP-A-9-126809, Patent Document 3; JP-A-7-131972, Patent Document 4; JP-A-9-133718, Patent Document 5; JP-A-9-145757, and Patent Document 6; JP-A-2005-3530).